Definition of: diapason

(dī′ə·pā′zən, -sən) noun
1. The basal melodic tone of a pipe organ; also, the stop producing it. In the open diapason the pipes are of metal and open at the top; in the stopped diapason the pipes are of wood and closed at the top.
2. A tuning fork, or the standard pitch given by a tuning fork.
3. In old Greek music, an octave.
4. Archaic Comprehensive or fundamental harmony; universal concord. [<L <Gk. dia pasōn (chordōn) through all (the notes)]